Ethanol made from cellulosic biomass is an alternative to petroleum-based liquid transportation fuels. However, large-scale manufacturing of cellulosic ethanol is hindered by the low density of cellulosic biomass. Experiments have shown that ultrasonic vibration-assisted (UV-A) pelleting could compress low-density raw biomass into high-density pellets, and pelleting temperature increased during pelleting process. However, pelleting temperature was not fully investigated. This paper reports an investigation on pelleting temperature in UV-A pelleting of wheat straw. The precision of temperature measurement was first evaluated. Relationships between pelleting temperature and pelleting time were then investigated. Also, the pattern of pelleting temperature distribution was evaluated by ranking the pelleting temperatures at six different locations in a pellet. Finally, effects of three input variables (ultrasonic power, pelleting pressure, and pellet weight) on pelleting temperature were discussed. Results reported in this paper are the foundation of a follow-up paper reporting relationship between pelleting temperature and pellet quality (density, durability, and sugar yield). (C) 2015 Elsevier Ltd. All rights reserved.